If you don’t do the valley right in the first place the metal is not going to save you…

I use metal in the valleys if it is requested, it is seldom needed.
If you choose to use metal in the valley, install the ice & water shield first then the metal over that.
If you don’t use Ice & water shield in your valleys you should use metal, and you must keep all of your nails a minimum of 6" away from the centerline of the valley.

an open metal vally is for looks only if you know how to roof. That said there are some cases where you need metal like cedar and slate roofs some heavy weight shingles like the Certainteed Grand Manor you should also use an open copper vally.But with a thirty year shingle it is not needed.

one more thing there mexiroofer, before you leave the
class room,
im not sure if this post was for your research paper
on the life span of different roof valley assemblys,
or if you simply want to know which one is easier to install.

ill answer both.

both valley specs will last plenty long enough.
no one will argue that.
the western cut is easier to install.
some will argue that.

my husband is the mexiroofer but I am trying to learn because I speak to the clients. He always does the cut down the middle whaytever that is called and it looks very nice and clean. However I was wondering how one decides so I could explain to customers who may have the same question. I must say it was very difficult for me when my husband decided that he wanted to go into business for himself because his English is limited and my knowledge of roofing was nil. I have since learned how to measure, order materials, write contracts etc. in a matter of months. I must say I am liking it more the more I learn. I am now learning how to price out siding jobs as well. Little by little. I come here often to check the posts and always get good answers to my questions (and some laughs). That is my husband doing the copper flashing on the cedar roof. Thanks guys.

in my area pladed valleys are the norm, we aren’t required to use icesheild but will if it is requested. most guys i know from up north like to do cut valleys and one i kinda like, when you run the low slope side atleast nine inches up and then come back pop a line and run a turn around and then 45 your dim. shingles up the valley never having to cut. they are always saying “3 layers protection”, lol yeah on one side, pladed valleys are double layer all the way, just takes someone who knows how to keep it centered. Open valleys are decrative mostly, i’ve installed some nice ones with copper. icey areas wouldn’t be a good place to run these prolly.